Compressional wave transmitter



Aug. 13, 1963 M. MA1-Ks 3,100,886

COMPRESSIONAL WAVE TRANSMITTER Filed April 27, 1959 2 .Sheets-Sheet 1 ATTORNEY Fild April 27, 1959 2 Sheets-Sheet 2 INVENTOR. CM eye/1 Ma/TJ ATTORNEY United States Patent O snsasss COMPRESSINAL WAVE TRANSMITTER Meyer Marks, Clarendon Hills, ill., assigner to Admiral Corporation, Chicago, lll., a corporation of Delaware Filed Apr. 27, 1959, Ser. No. 809,052

3 Claims. (Cl. S40- 15) This invention relates to signal apparatus for producing sound waves of predetermined frequency or frequencies, `and it is an object of the invention to provide im-` proved apparatus of that character.

In the growing art of remote control apparatus `for television receiver sets, it is common practice to employ compressional or ultrasonic waves of predetermined frequency yas 1a means of transmitting a signal or a plurality of distinguishable signals from `a remote transmitting station to a receiver station within the television receiving set. These ultrasonic waves are of frequencies well above the upper hearing limit of the human ear, This eliminates objectionable audible sound during signal transmission and substantially eliminates the possibility of unintended 4operation of the receiver set control systeni by audible noise. Apparatus constructed in accordance with the present invention is particularly well adapted to such use ybut it will be appreciated by those skilled the art that the apparatus is of broad applicability.

Prior art apparatus `of this 'general type has suffered from `one or more of a number of objectionable characteristics. Among these are objectionable bulkiness of the transmitting unit, short battery life where batteries are employed las a power source, unreliahility of operation, delayed operation and high oost. As opposed to this, apparatus constructed in accordance with the present invention may be very compact, requires such |a small amount of power that the life of a battery incorporated in the apparatus is substantially the shelf life of the battery, is instantaneously operative and is inherently reliable in operation and economical to manufacture.

Accordingly, it is an other `object of the invention to provide improved apparatus for producting ultrasonic Waves of one or more predetermined frequencies which is small in size and yeconomical yto manufacture.

It is a further object of the invention to provide improved `apparatus of the character described above which is inherently reliable in operation.

It is a still yfurther object of lthe invention to provide improved apparatus of the character described above which employs one or more piezoelectric transducers as an ultrasonic propagating means.

Another object of the invention is to provide improved apparatus of the character described above which employs :a transistor asa signal translating device.

Further features of the invention pertain to the particular arrangement of the elements of the ultrasonic producing apparatus, whereby the above outlined and additionl features thereof 'are attained.

The invention, both las to its organization 'and method of operation, together with further objects and advantages thereof, will best be under-stood by reference to the following speciiication, taken in connection with the -acco-mpanying drawings, in which:

FIGURE 1 is a circuit diagram illustrating an embodiment of the invention for` producing ultrasonic waves of a single predetermined frequency;

FIGURE Z is a circuit diagram of an embodiment of the invention `for producing ultrasonic waves of selected predetermined frequencies;

FIGURE 2a is a partial circuit diagram illustrating yan alternative to the embodiment of the invention shown in FIGURE 2, and

FIGURE 3 is a circuit diagram of another embodiment 2 of the invention for producing ultrasonic Waves of selected predetermined frequencies.

As indicated above, the present invention is well adapted to the ygeneration of ultrasonic Waves for actuatinga remote receiving device which controls a television receiver in response to Ithe generation of such ultrasonic waves. The embodiments of the invention illustrated in the drawings and described below are specifically adapted to such use, but it will Ibe readily `appa-rent to those skilled in the art that the invention is of broad applicability with or without modification or adaptation of the illustrated embodiment thereof.

In the embodiment of the invention illustrated in FIG- URE 1, apparatus is provided for producing ultrasonic waves of a single predetermined frequency, but which, with slight modification may produce ultrasonic waves of two or more frequencies. The specic -frequency preferred is 40,000 cycles per second, this frequency being well la-bove the audible range whereby it cannot be heard and is not readily duplicated 'in casual noise. The ultrasonic wave produced by this apparatus may, for example, be employed to actuate control apparatus which advances the channel selecting switch of `a television receiver successively from one channel to Ithe next in a manner Well known in the art.

Included in the signal generating apparatus of FIG- URE l is ya piezoelectric transducer 10 which may be of conventional form and, therefore, is not described in detail herein. For the purpose of appreciating the present invention it is necessary to understand only that the transducer 10 lincludes a piezoelectric element with suitable electric terminals and physical mounting Lsuch that electrical excitation of the piezoelectric element through the electric terminals causes mechanical vibration thereof which is transmitted to the surrounding air. Where the term piezoelectric transducer 4isemployedl herein, it is intended that it be interpreted broadly to include microphones, such microphones incorporating not only genuine crystals, either natural or artificial, but materials such as barium titanate, which do not qualify 'as crystals in the technical sense.

As is also well under-stood in the art, any' given piezoelectric element has a natural or resonant frequency. 'Ilhe piezoelectric element included in the transducer 10 is selected to have a resonant frequency equal to the frequency of the sound Wave that is intended to be generated. In the specific embodiment of the invention illustrated in FIGURE 1, the piezoelectric element of the transducer 10 should, therefore, have a resonant frequency of 40,000 cps.

The transducer lll is connected across `the terminals of an inductance coil 11, as shown, to form an LC circuit also having a resonant frequency of I40,000' cps. One form of transducer which has Ibeen employed in the circuit of FIGURE 1 has a capacity of v932 micro-microfarads. An finductance of 17 mlllihenries for the coil 11 in cooperation with such a transducer produces an LC circuit resonating at 40,000 c.p.s. The coil 1-1 includes an adjustable slug such that it may be tuned in a well known manner. Preferably, the coil `has 'a relatively high Q factor (eg. 5G) lfor reasons well known in the `ar-t. tlf desired, additional capacity may be arranged in parallel with the transducer in keeping with various parameters of the circuitry.

The LC circuit formed by the transducer 10 and the coil 11 may be excited iby various forms of apparatus. In the preferred embodiment of the invention, the exciting lappara-tus includes .a junction type transistor 12, which maybe a 2N217 transistor, and a power source consisting of a three-volt dry cell 13, One of the output leads of the transistor 12, namely, the collector lead 14, is connected lto Ia tapped point on the coil 11, and the negative terminal @of the battery :13 is .connected through a switch 15 to another tapped point on the coil 11, the positive terminal of the battery 13 being represented as connected to ground. The output circuit yof the transistor 12 is completedv by connection of the other output lead, namely, 4the emitter lead 16', to vground through a bias resistor 17 and la parallel-ing bypass capacitor 18. Abypass capacitor 19 is connected between -ground and the negative (terminal of the battery 13.

A` feedblack'circuit is connected to the controllead of :the transistor 12, namely, the base lead 20. This reedback circuit connects a point 21 of the LC circuit to the base lead 20 of the transistor through a resistor 22, the base lead 20 being connected to ground through another resistor 23. It Iwill be apparent that the resistors 22 and .'23 comprise `a voltage divider. A coupling capacitor24 is arranged across the resistor 22. -It will be seen that the oscillator thus provided is ofthe Hartley type. As will be that with the coil 11 adjusted suchl that the LC circuit,

comprising the coil 11 and transducer 10, resonates `at the reso-nant lfrequency of the transducer, an ultrasonic wave of substantial magnitude may be emitted by the transducer with a very small power input. The simple three-volt dry cell which is recommended to power the circuit will have long life since the circuit draws very litt-le current `and since the dry cell is disconnected from the circuit when the apparatus is not in operation. At the same time, there is no delay in operation of the circuit -since the transistor is instantaneously opera-tive. It will also be -seen that the apparatus is inexpensive to manufacture since it requires in addition to a small number of conventional resistors 'and capacitors only a dry cell, atransis-tor, a slug ltuned coil and .a piezoelectric transducer. Y

YWh-ile the values of the various resistors and capacitors employed in the circuit are not critical, a list of recommended values is given below: Y

' The [apparatus of FIGURE 1 :is particularly suited to the production of ultrasonic waves of one predetermined rfrequency. However, as will readily be recognized by those skilled in the art, .the LC circuit comprising the coil 11 and the ltransducer 10 may very simply be forced to oscillate at frequencies differing by a few hundred cycles yfrom the 40,000` cps. resonant frequency o-f the LC circuit and of the transducer. Two or more frequencies may thereby be produced to convey different signals to a highly discrimina-tory receiving station. Since such modification of the `frequency output of the apparatus may be accomplished by various well known means, and since such means do not constituteV a feature of the present invention, they are not shown, or described in detail herein.

The embodimentof the invention illustrated in FIG- URE 2 is much the same as the embodiment of FIG- URE 1, with the exception that it includes ya plurality of piezoelectric transducers for producing ultrasonic waves of a plurality of predetermined frequencies, fand switch means for selecting a transducer and, hence, a frequency of ultrasonic waves. The plurality of different frequencies of these waves may be employed to initiate four different control operations ata receiving station. F or example, as applied to remote control of a television receiver, the four diferentfrequency signals may control the on-od switch, the volume control, clockwise rotation of the channel selecting switch, .and counterclockwise rotation of the channel selecting `switch. Where a single broadband receiver is provided at the receiving station, followed by apvparatus which discriminates between the four -diierent signal frequencies, it is preferred that the Ifour signal frequencies differ by relatively small percentages. In one application of the :apparatus illustrated in FIGUR-E 2, it bas been found desirable that .fthe -four frequencies be 38,285, 39,285, 40,805 and 41,805 cycles per second.

iin yFIGURE 2 lfour piezoelectric transducers 31, 32, `33 and 34 are arranged with one terminal of each connected in common to one end of an inductance coil 35, the latter preferably being slug tuned. The coil 35 is selectively coupled with any one |of the transducers 31--34 in Ithe manner described below such that the coil 35 'and the select-ed transducer form `an LC circuit which resonates at the resonant frequency of the corresponding transducer. In the interest of economy, the four piezoelectric transducers fare substantially identi-cal with the exception of their resonant frequencies and, accordingly, their capacitive values are substantially equal. Since lthersarne inductance coil 35 is to be employed in each of the four possible LC circuits, capacitors 32a, 33a and 34a lare :arranged in parallel with the transducers 32, 33 and 34, respectively, to provide the necessary additional capacity to tune the corresponding LC circuit `to the resonant frequency of the corresponding transducer.

The transducer and associated capacitors are ,selectively coupled to the inductive coil 35 to form LC circuits of the desired resonant frequencies by means of switches 41, 42, 43 and 44. More particularly, closingof contacts 41a and 41b of switch 41 connects the transducer 31 across the coil 35 to form an LC circuit resonating at the resonant frequency of the transducer 31. Similarly, closing of the contacts 42a and 42h, or 43a and 43h, or'44a and 44b completes an LC circuit incorporating a transducer 32, 33 or 34, respectively, along with its associated capacitor and the coil 35.

Each of the switches 41-44 preferably includes` three contacts whereby closing of the a and b contacts of any of the four switches to form an LC circuit is accompanied by closing of these contacts with a c contact, whereby the selected LC circuit is connected to the negative terminal of a battery 45, whosepositive terminal is represented as being connected toground.

Switches such as the switches 41-44 are well known in the art and, accordingly, are not described in detail herein. For the purpose of explaining the present invention, it is necessary only to point out that all three contacts of any of the switches are brought into electrical contact with each other upon actuation of the switch, whereby the a and b contacts are electrically connected to complete an LC circuit, and these are connected to the c contact to connect the LC circuit to the power source.

A transistor 47 is provided across the output leads of which the battery 45 and a selected LC circiut are connected by the closing of any of the switches 41-44. More specifically, the collector lead 48 is connetced to a tapped point on the coil 35, as shown, andthe emitter lead'49 is connected to ground through a bias resistor 50 and a bypass capacitor 51. Another bypass capacitor 52 is connected between the LC circuit and ground, as shown.

KIn this embodiment of the invention, feedback is providiec; by a coil 54 which is inductively coupled with the coi 5. the transistor, as shown, ,andto the intermediate point of a voltage divider extending between one end of the coil 35 and ground. The voltage divider comprises a pair of resistors 56 and 57, the latter of which is paralleled by v a bypass capacitor 58.

Operation of the apparatus illustrated in FIG. 2 is believed to be obvious. If the switch 42, for example, is closed, the contacts 42a and 42h are closed to complete an LC circuit. The total capacity of the crystal microphone 32 and lthe capacitor 32a coupled with the inductance of the coil 35 provides an LC circuit which resonates at the resonant frequency of the transducer 32. Con- F[he coil 54 is connected to the base lead 55 of e nection of the contacts 42a and 42h to the contact 42e completes the output circuit of the transistor 47. Feedback is provided by the coil 54 such that the circuit may oscillate at a frequency determined by the selected LC circuit. The transducer 32, accordingly, emits an ultrasonic wave of substantial magnitude and of a predeteridentical to that disclosed in FIG. 2. In the embodiment of FIG. 2a, the coil 35, the transducers 31-34, the switches 41-44 and the battery 45 may be identical to the corresponding parts employed in the apparatus in FIG. 2. In particular, the transducers 31--34 may be of equal capacity but of different resonant frequencies. The various LC circuitsobtainable by selective closing of any of the switches Lil-44 are tuned to the resonant frequencies of the corresponding transducer by means of inductive coils 3212, 3319, and 34h, which are connected between one end of the coil 35 and respective ones of the switch contacts 42h, 43h, and 44h. The coils 32h-Sb are of different inductive values whereby addition of the inductance of any one of these coils to the inductance of the coil 35 provides a total inductance which will resonate with the capacity of the lcorresponding transducer at the resonant frequency of the corresponding transducer. The coils 32b--34b comprise means, alternative to the condensers 32a-34aof FIG. 2, for tuning the various LC circuits to the resonant frequency of the corresponding transducer.

The embodiments of the invention illustrated in FIGS. 2 and 2a permit the generation and transmission of ultrasonic waves of four substantially differing frequencies with a minimum of power and with a single signal translating device. The four frequencies suggested above differ in steps of approximately two and one-half percent and four percent. With these selected frequencies, a single broad-band received may accept al1 four signals and readily distinguish between them. It will be appreciated by those skilled in the art that the transmitting apparatus of FIGS. 2 and 2a may, if preferred, generate and transmit ultrasonic waves of much more widely differing frequencies.

Recommended values for the various resistors and capacitors employed in .the circuits of FIGS. 2 and 2a are tabulated below:

It will be understood that the Values of the capacitors 32a- 34a are selected to produce resonance of the associated LC circuits at the desired frequencies, in a manner well understood in the art.

The embodiment of the invention illustrated in FIG. 3 differs from that illustrated in FIG. 2 primarily in that the plurality of transducers fri-34 of FIG. 2 are replaced in the oscillator stage of FIG. 3 by conventional capacitors, and an amplifier stage incorporating a second signal translating device is provided which is excited by the oscillator stage. A single transducer is employed in an LC circuit across the output leads of the second stage signal translating device. The single transducer, preferably resonant at 40,000 c.p.s., is readily driven at the four frequencies suggested above in connection with the embodiment of FIG. 2.

Since the entire iirst stage of the embodiment of FIG. 3 is identical to that of `the embodiment illustrated in FIG. 2 with the exception of the substitution of conventional capacitors 61, 62, 63 and 64 for the transducers 31-.34 of FIG. 2, this stage will not be redescribed.

6 Each element of the oscillator stage of FIG. 3 is identified by the same reference numeral as in FIG. 2.

It Will be noted that the capacitor 61 which replaces the transducer 31 isnot connected to the contact 41a of the switch 41 but is, instead, connected directly across the coil 35. This capacitor is, therefore, included in all four LC circuits. Accordingly, the capacitors 62, 63 and 64 need be only of such`value as to add to the capacitance of the capacitor `61 to provide total capacitance which will resonate with the coil 35 at the desired frequencies. With this arrangement, the coil 35 may be tuned by slug adjustment with the capacitor 61 such that this basic LC circuit resonates at the highest of the desired frequencies. Discrepancies in the capacitive values of the capacitors 62-64 because of manufacturing -tolenance then have less effect upon "the total capacity of the LC circuits obtained by closing any one of the switches 42, 43, or 44 than would be the case if the capacitors 62-64 comprised the total capacitance of these LC circuits.

The second stage of this embodiment of the invention includes a piezoelectric transducer 70 arnanged across a coil 71. The capacitance of the transducer `'70 and the inductance of the coil 71 form an LC circ-uit resonating at 40,000 c.p.s., this also being the resonant frequency of the transducer 70E. A transistor '72 of the junction type has its collector lead A'74 connected to a tapped point on the coil 7ll. Upon the closing of any of the switches 4in-44, one end of the coil 71 is connected through a resistor 75 and the b and c contacts of the selected switch to the negativeterminal of the battery 45. The same end of the coil 71 is connected to ground through a bypass capacitor 76. The output circuit of the transistor 72 is completed by connection of the emitter lead 77 to ground through a resistor '78. A bypass capacitor 79 parallels the resistor 78.

A signal is fed from the oscillator stage to the output stage of this embodiment of the invention through a lead 80 which connects to a tapped point on the coil 35 in the output circuit of the oscillator stage. This Ilead connects to one end of a voltage divider comprising a pair of resistors -81 and .812, the other end of the voltage divider being connected to ground. The resistor 81 is bypassed by a capacitor 83, and the base lead 84 of the transistor 72 is connected to the intermediate point of the voltage divider.

Recommended values for the various resistors and capacitors employed in the second stage of the circuit of FIG. 3 are tabulated below:

`RTS-47 ohms CTG-0.1 mfd. R78-47 ohms C79`-0.1 mfd. RSI-200K IG83-150 mmfd. RSZ-5K As Iwill be apparent to those skilled in the art, the oscillator stage is unaffected by the output stage, and, accordingly, oscillates at a frequency determined by the selected LC circuit of the first stage. A signal is fed from the oscillator stage to the output stage through the lead 80 whereby the output stage is made to oscillate at a frequency dictated by the oscillator stage. While the LC circuit, including the coil 71 'and the transducer 70 contained in the output circuit of the second stage, tends to oscillate at 40,000 c.p.s., it is readily forced to resonate at a frequency as low as 38,285 c.p.s., or as high as 41,1805 c.p.s., as dictated by the oscillator stage. Accordingly, a single transducer 70` may be made to propagate ultrasonic Waves of various frequencies which differ suiiiciently that they are readily distinguishable by a receiving station.

Various embodiments of the invention have now been described which produce compressional or ultrasonic Vto any desired extent.

cation, to produce ultrasonic waves of two or more frequencies which differ by relatively small percentages. Theembodiment illustrated in FIG. 2 employs a plurality of transducers for producing ultr-asonic waves of a plurality of frequencies which may diifer from each other The embodiment illustrated in FIG. 3 employs -a single transducer but two signal translating devices. This embodiment may produce ultrasonic waves of a plfurality of frequencies which may differ from each other by substantial percentages.

The apparatus included in the various illustrated embodiments of the invention may readily be arranged in a very small housing. As lwill be readily apparent to those skilled in the art, the apparatus incorporated in the illustrated embodiments of the invention is inherently reliable in operation and will produce ultrasonic waves of frequencies varying only minutely from preselected values as a result of changes in temperature, humidity, and battery strength.

The invention is well adapted to the use of transistors as signal translating devices and accordingly may be instantaneously operable even though the power source is idle except -when the apparatus is actually producing sound waves. This, combined with the tact that the apparatus draws'very little power even when actually producing ultrasonic Waves, assures battery life substantially equal to shelf life of the battery where a battery is used as the power source. 'It will 'also be apparent that Wthe illustrated embodiments of the invention incorporate relatively inexpensive components whereby the total cost'of the sound producing apparatus is low in spite of the above referred to and other desirable characteristics of the apparatus.

- It will be apparent to those skilled in the art that many modiications of the illustrated apparatus may be effected without departing from the spirit of the invention. By way of example electron tubes may be employed where desired in place of the suggested transistors. ln general various types of exciting circuits may be employed and various forms of apparatus may be employed for controlling oscillator frequency.

Accordingly, while there has been described what are at present considered to be the preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended tov cover in the appended claims'all suchmodiiioations as fall within y the true sprit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A portable transmitter for generating and transmitting ultrasonic compressional waves of predetermined frequency comprising; a transistor having a base, an emitter and ja collector; a tank circuit coupled in the emittercollector circuit of said transistor, said tank circuit being resonant at said predetermined frequency and including emitter circuit of said transistor;` said base being connected to a point on said voltage divider, and being supplied both a direct current potential `from said battery source and a feedback potential from said tank circuit, whereby said transistor oscillates `at the frequency of resonance of said tank circuitand said piezoelectric transducer element transmitssaid ultrasonic compressional waves. l Y

2. A low powered battery operated portable transmitter for `generating and transmitting ultrasonic compressional waves of predetermined frequency comprising: a transistor` having anemitter, base, and collector electrode; a resonant tank circuit, including `an inductor and a capacitive piezoelectric transducer for transmitting compressional waves responsive to electrical excitation thereof, coupled between s-aid collector and said emitter electrodes; a portion of said resonant tank circuit being coupled between said collector andV said base electrodes to provide a'feedback connection for feeding back a portion of the voltage across said resonant tank circuit to cause oscillation of said transistor; biasing networks for said Ibase fand said emitter electrodes; a battery source of electrical power having aV first terminal connected to said collector electrode through said resonant tank circuit, and la second `terminal connected to said base andy said emitter electrodes through said biasing networks respectively; said transistor oscillating at thefresonant frequency of said tank circiut upon connection of'said battery source thereto, whereby said capacitive piezoelectric transducer transmits corresponding compressional waves of Vsaidv predetermined ultrasonic frequency.

3.'A low powered battery operated portable transmitter as claimed in claim 2 further including another capacitive piezoelectric transducer for resonating at a different predetermined ultrasonic frequency with said inductor land means for selectively including said transducers in said resonant tank circuit.

References Cited in the iile of this patent UNITED STATES PATENTS 

1. A PORTABLE TRANSMITTER FOR GENERATING AND TRANSMITTING ULTRASONIC COMPRESSIONAL WAVES OF PREDETERMINED FREQUENCY COMPRISING; A TRANSISTOR HAVING A BASE, AN EMITTER AND A COLLECTOR; A TANK CIRCUIT COUPLED IN THE EMITTERCOLLECTOR CIRCUIT OF SAID TRANSISTOR, SAID TANK CIRCUIT BEING RESONANT AT SAID PREDETERMINED FREQUENCY AND INCLUDING AN INDUCTIVE ELEMENT AND A CAPACTIVE PIEZOELECTRIC TRANSDUCER ELEMENT; A BATTERY SOURCE FOR SAID TRANSISTOR; A VOLTAGE DIVIDER; MEANS, INCLUDING A PORTION OF SAID INDUCTOR FOR COUPLING SAID VOLTAGE DIVIDER TO SAID BATTERY SOURCE SO AS TO SUPPLY VOLTAGE TO SAID DIVIDER AND TO THE COLLECTOREMITTER CIRCUIT OF SAID TRANSISTOR; SAID BASE BEING CONNECTED TO A POINT ON SAID VOLTAGE DIVIDER, AND BEING SUPPLIED BOTH A DIRECT CURRENT POTENTIAL FROM SAID BATTERY SOURCE AND A FEEDBACK POTENTIAL FROM SAID TANK CIRCUIT, WHEREBY SAID TRANSISTOR OSCILLATES AT THE FREQUENCY OF RESONANCE OF SAID TANK CIRCUIT AND SAID PIEZOELECTRIC TRANSDUCER ELEMENT TRANSMITS SAID ULTRASONIC COMPRESSIONAL WAVES. 